The algebraic sum of all voltages in a loop must equal zero
Ttailspin
Posts: 1,326
I sat and stared at that statement for 5 minutes before gathering the courage to scroll down the page to look at the 'all-gee-bray-ick' stuff.
This page has a relatively painless explanation , complete with illustrations and easy to follow text..
Voltage dividers, Who would have thunk it? Man, did that Kirchhoff guy ever get any sleep??
Most likely, this stuff is 'old hat' for many of you, But, to a Journeyman carpenter, It's a genuine revelation in electronics exploration.
And thought it might be nice to share with you...
-Tommy
This page has a relatively painless explanation , complete with illustrations and easy to follow text..
Voltage dividers, Who would have thunk it? Man, did that Kirchhoff guy ever get any sleep??
Most likely, this stuff is 'old hat' for many of you, But, to a Journeyman carpenter, It's a genuine revelation in electronics exploration.
And thought it might be nice to share with you...
-Tommy
Comments
big head of water large voltage
thin pipe - high resistance, fat pipe low
gate valve or tap - switch or transistor or fet???
A tank is a capacitor
mmm whats an inductor - a balloon???? no....
Dave
This just blew my mind. All the other electricity-as-water stuff was familiar to me, but the paddlewheel with inertial mass thing just really opened up LC circuits for me - I never could really figure out how I could make that analogous to water because of the L side. Paddlewheels and tanks... I can see it! :-)
Something I've noted before: Somebody once described to me a circa 1968ish space mission that was to send a vehicle as close to the sun as possible. Because electronics couldn't take the heat for long, it was to be flown completely by fluidic logic. I was told that they had machined an incredible number of little hydraulic valves that would work like fluidic transistors and the whole thing would work via logic circuits made for high temperature fluids. I always wanted to ask how the communication system worked - smoke signals maybe???
I think you are taking about Fluidics. A cunning way of building logic gates with fluids. The really cunning part is that they have no moving mechanical parts like hydraulic valves. See here for a description: http://en.wikipedia.org/wiki/Fluidics Amazingly also used to build audio power amplifiers it seems.
I have seen logic built from more regular hydraulic valves and such, a horrible mess of pipes and valves controlling a factory process. Designed before computers were applied to such problems. There was no one left in the company who understood how it worked they just kept on building machines with the same design for years.
Back in tech school I did get to build a divide by four binary counter using pneumatic rams and spool valves just for fun. It made a great sound as it operated.
Actually the above statement may be a bit too simple. What you have here is a complete system in the form of a circuit. When all the forces equal zero, the system is stable. And excess of force would damage the circuit, less than enough force and the circuit may not be active in the desired manner.
And a 'zero-sum game' is really any game where there is a balance between winning and losing, such as checkers or table tennis. Somebody has to win and somebody has to lose, unless there is a draw. The term really doesn't apply to electronics or physics.. it is game theory.
The Zero-sum game doesn't apply to economics, either. If one kid has bread and the other has peanut butter, they can each exchange a portion of their holdings and yet both of them win (peanut butter sandwiches). Unfortunately many people assume economics is a zero-sum game all the time. Example: if money is being spent on scientific research, then it must mean money is being "robbed" out of the economy somewhere else. In reality, there are multiplier effects, etc. that can help everyone in the economy to win, especially in the long run. Similarly, there are other effects and situations that "make sense" to the zero-sum game mindset but that can cause everyone to lose, especially in the long run.
Economists point to the growing population, the generally improved situation of many of them compared to centuries ago and say look "With all this economic activity and global trade going on the human population is healthier, has better diet, lives longer has better living conditions etc etc etc."
They argue that this is not a zero sum game because all this activity "grows the pie". As you hinted diverting money to research does not rob the rest of the population because historically such research has benefited everybody. So far so good.
The problem in my mind is the physics of the thing. When we have consumed all our energy reserves, depleted all essential resources, turned every available square inch to desert and generally polluted the place then, that's it. No more pie to grow. End of game.
This endless "pie growing" or economic growth cannot go on for ever.
On the other hand, to me the "zero sum game" concept belongs to a branch of mathematics, game theory. Where it has a very rigorous meaning. It has no place in describing economics which, I have to be polite, is just hand waving.
Space is really big, and pretty much all of it is hostile to human existance. I hold out little hope of ever getting anywhere "safe".
I also start to think that we just don't have the resources on the entire planet to pull off such a stunt.
I have thought about this a great deal, and I think you are unduly pessimistic. Greatly so. There are some resources of which we have a virtually endless supply. Sunlight, nuclear, brine (and the many elements in it), carbon, aluminum (or aluminium if you wish), silicon, iron, etc. For other elements, we can do far more that we are doing to limit their use and maximize their recovery (the seafloor, covering 7/10th of the planet, is virtually untouched). Obviously what we do, and how we do it, will evolve. But our ability to keep doing it is almost unlimited.
Changing themes: In the course of pursuing a degree in mechanical engineering, my classmates and I quickly abandoned mechanical analogs. Before long, all we talked about in some classes were resistances, capacitances, and inductances. We did this even when we were dealing with purely mechanical systems. (I still remember sitting in ME435, reveling in the irony.) Both the students and the professors exhibited a preference for going about it that way.
I was struck by the analogy too when I first heard it from one of my office mates in grad school (now a prof at MIT). Why else do we get an education? It is analog phenomenology we are talking about, and as one can discern from the direction this thread has taken, analogies can be extended far afield. The flip side is that they break down rapidly when examined in detail. The hydraulic analogy too can taken to a point, but not an iota further.
There is a rather nice diagram of the paddle-wheel analogy for an inductor on this wikipedia page.
The paddle-wheel is a contrivance, as opposed to a consequence of simple physical law. The inertia of moving water itself is better, a physical aspect of the flow. The hydraulic-inductance can be increased by a long pipe (perhaps coiled up). The long pipe has resistance of course, losses, just like a real inductor. In any case, you can appreciate the kick in pressure that occurs when a valve is suddenly closed. That is the principle of switching-type voltage converters.
In my little mind, the concept of economics not being a zero-sum game does not lead to the conclusion that unfettered population growth is a necessary or desired result. Far from it. I'm not a fan of cities and therefore dwell among the tobacco-chewing moonshine-gargling backwoods troglodytes to evade the over-crowding of the cultured urban areas. Having said that, I can at least imagine the possibility that the human species, or some distant relative of it, might someday figure out a way to live within its planetary means and yet still advance technologically, ecologically, psychologically, neurologically, astronomically and socially. Might even figure out a way to keep the sun from overheating a mere billion years from now.
Maybe it's ironic, but most of the economists I hear proclaiming that they merely "want to grow the pie bigger for everyone," are usually of the Wall Street variety who are trying to make a case for why they need even bigger tax cuts than they're already getting.
Unless Tommy protests, I say we run this sucker off the rails as far as she'll go!
Yeeeee... ha!
Who needs "safe". We need to be challenged to grow and advance. We have the resources and the knowledge to get into space, what we lack is the will to do so. It may be costly at present but the cost will go down, particularly when we start to use the resources available in space.
Many people presume Economics is a science, there is even the term 'political science'. That is truly an oxymoron of huge proportions. Economics and political science are ledgerdermain at its best. Who needs a magic show when you can manipulate voters?
The water and electricity analogy holds because the underlying system of physics applies Newtonian principles. For about 3 centuries now, society has advanced prosperity and technology that has been highly dependent on the spread of ideas and concepts that Newton presented.
Balancing forces is also used in the design and construction of structures, such as buildings. But in that case, the forces are gravity, bending, shear, wind, live load, and dead load.
We seem to be ignoring what the Current is doing in the same circuit that all the Voltages (or Forces) are balanced to zero. the constant interplay of Force and Current are important to understanding electronics.
If you really want to leave the planet, go! What's stopping you?
And so, both kids now have peanut butter and bread and eat lunch... the end result is they have destroyed all their capital. Not particularly a good analogy.
No arguments with that. You need to be manipulative, devious, and somewhat unethical to be a successful politician. That's why so many lawyers are attracted to politics.
Current was not really ignored, it was just not very relevant to the point that was being made initially.
Gravity!
http://openbookproject.net//electricCircuits/
Consider a battery that is not connected to anything with terminals N and P.
Now, there is a path from from N to P and from P back to N and you can measure the voltage difference along each step of that path. The sum will of course be zero.
This statement is a rather deep property of the electric field regardless of anything moving within it.
The deep property being Maxwell's equations, specifically Faraday's Induction Law: The line integral of electric field around a closed path equals zero. (fine print, so long as it is within the limit of insignificant induced field due to rate of change of magnetic H field).
(An aside, I just received an email from a Portuguese-speaking colleague, who thought we might need a Faraday jail around a device we've been working on).
Here is a simple circuit that often gives people trouble.
KVL says the sum of voltages around the circuit is zero, VS+VL-VB = 0. Now close the switch for an instant of time and then open it. What does KVL say about all three conditions? Everyone knows there will be a kick of voltage from the inductor when the switch opens.
Salient points:
-- The circuit model with just the three components shown will break down, literally.
-- It helps the analysis of KVL if you put a virtual capacitor across the switch or across the inductor.
-- The sum of voltages around the loop is zero only insofar as the big loop itself does not have significant inductance or is so large that it acts as a radiator of radio waves. That is the fine print on KVL. KVL is a simplified level of abstraction.
-- The inductor shown in the circuit is a lumped element that obeys dV = L dI, so it can be analyzed in a circuit using KVL and KCL. However, the inductor within itself obeys the expanded version of Faraday's Induction Law, where the electric field integral depends on the linked magnetic field.